1. Field of the Invention
The present invention relates to a process for growing crystals at an enhanced rate, particularly crystals of a metal oxide. In a particular embodiment, the present invention relates to a process for growing large, i.e. greater than about 150 Angstroms, crystal size, hydrated aluminas at an enhanced rate.
2. Description of the Background
There are many instances in which it is desirable to obtain large, uniform crystals of a given substance. One obvious case is the production of gem stones by crystal growth in an attempt to obtain flawless gem quality crystals. Also, high purity, uniform flawless single crystals of sufficient size are finding increasing utility in lasers, solid state electronics and other high tech fields.
Another application is in the production of Uniform crystal size ceramic particles for use in high tech ceramic parts. It is known that use of ceramic powders having certain crystal size/particle size allows for more controlled and uniform particle packing when preparing the ceramic green body. For example, too large a particle size results in non-uniform packing of particles during formation of the ceramic green body. This results in flaws and limited mechanical strength in the finished ceramic part. Likewise, if the particle size is too small, i.e. less than about 0.2 microns diameters, it again becomes difficult to obtain the desired, uniform packing in the green body. This is primarily due to difficulty in completely dispersing the small particles at concentrations which are preferred for commercial ceramic part forming processes such as slip casting.
In U.K. Patent No. 838,575, entitled "Method of Growing Corundum Crystals", there is disclosed a method of growing large single crystals of corundum of a size suitable for gems from seeds in aqueous media under high temperatures and pressures. In the method disclosed in the British patent, which is a batch method, the seed crystals, contained in a pressurized vessel, are subjected to a mass of alumina containing nutrient adapted to supply corundum for growth of the seed crystal, both the seed crystal and the nutrient mass being in contact with an aqueous medium which is present in an amount sufficient to occupy at least sixty-five percent of the free space within the container at room temperature. The method disclosed in the British patent is, as mentioned, a batch process which does not rely on uniform dispersion of feed material to supply nutrient for crystal growth, relies on a one time, single charge of nutrient material, fails to recognize the advantage of "feeding" crystals having an average crystal size less than the seed crystal in order to enhance growth of the seed crystal and requires a temperature differential between the nutrient mass and the seed crystal.